1. Field of the Invention
The present invention relates to a four-cycle engine including a secondary air supply passage for introducing secondary air into an exhaust port.
2. Description of the Background Art
Japanese Patent Laid-open No. Hei 9-324624 shows a secondary air supply passage for introducing secondary air into an exhaust port of a cylinder head. The secondary air supply passage connects a reed valve chamber provided in the cylinder head cover to the exhaust port provided in the cylinder head. The connecting section between the cylinder head and cylinder head cover is sealed with a knock pin.
It is known that a positioning knock pin is used to position a cam holder in the cylinder head. Further, there are some structures that use a part of a bolt hole for tightening the cam holder and provide a knock pin at another position apart from the bolt hole.
Incidentally, in the case where the bolt hole is used as a knock pin for positioning the cam holder, it is impossible to bring the bolt close to the camshaft, as the diameter of the knock pin becomes larger. Moreover, making the positioning knock pin separate from the bolt hole will necessitate a dedicated boss, thereby increasing the weight of the engine.